1. 4-1 Classifying Triangles
Objectives:
The student will be able to:
1. Identify and classify triangles by
angle measures and side measures.

2. Classify Triangles by Angles:
Parts of a Triangle:
Sides
Vertices
Angles
Classify Triangles by Angles:
Acute triangle – all angles are acute (<90°)
Equiangular triangle – all three angles are congruent (=60°)
Obtuse triangle – One angle is obtuse (>90°)
Right triangle – One angle is right (= 90°)

3. Classify Triangles by Sides:
Scalene Triangle – No two sides are congruent (0 sides )
Isosceles Triangle – At least two sides are congruent (2 sides )
Equilateral Triangle – All three sides are congruent (3 sides )

4. Example 1: Classify each triangle as acute, equiangular, obtuse, or right.

5. Example 2: Classify each triangle as acute, equiangular, obtuse, or right.

6. Example 2: Classify each triangle as equilateral, isosceles, or scalene.

7. Example 2: Classify each triangle as equilateral, isosceles, or scalene.

8. Example 3: Find the measure of each side of equilateral ΔRST with and
All sides are congruent.
What now?
Substitute for x on each side.
2x + 2 = 3x
-2x
2x + 2 3x
5x - 4
2 = x
= 2(2) + 2
= 3(2)
= 5(2) - 4
= 4 + 2
= 6 =
= 6
= 6

9. Example 4: Find the measure of each side of equiangular ΔABC with vertices A(-1, 5), B(6, 1), and C(2,-6). Classify the triangle.
= 11.4
Isosceles
= 8.1
= 8.1